There are different types of inhalers on the market. A pressurized Metered Dose Inhaler (pMDI) releases a fixed dose of substance in aerosol form. A powder inhaler generally releases a dose of powdered substance entrained in an air stream. In a powder inhaler the powder may be provided in a bulk container of the inhaler from which doses of powder are metered for dispensing. As an alternative to a bulk container, powder inhalers may comprise a single compartment or a plurality of compartments for containing one or more discrete doses of powdered substance. Such compartments may take the form of sealed blisters in a blister pack, a cavities-containing strip joined to a sealing strip or other suitable forms.
EP 1 220 698 discloses an inhaler for medicament in powder form. The medicament is arranged in the inhaler in a number of enclosures. When the airflow in the inhaler reaches a certain threshold value, a breath-activated activating means causes an elongated hollow body to pierce the enclosure so that the medicament is accessed. This is, for example, illustrated in FIGS. 3-6 of EP 1 220 698. After the medicament has been inhaled, the user closes a mouthpiece cover, which leads to retraction and latching of the hollow body into a firing position, and also movement of the enclosures one step. However, with that type of inhaler, if the mouthpiece cover is not properly closed, there may be a risk of the hollow body becoming retracted and latched although the inhaler has not been completely indexed to the next enclosure. Thus, the next time the user wants to inhale, the hollow body may risk either entering the same enclosure or just hit an intermediate portion between two enclosures, without delivering any medicament.
WO2009/008001A2 discloses a dry powder inhaler having a breath actuation feature. Opening a mouthpiece cap energises a spring. On inhalation, a flap is moved which triggers the release of the spring, driving a mechanism to (i) puncture a foil sealed medicament cavity and (ii) ratchet an indexer around a set of ratchet teeth on the periphery of a disc of medicament cavities. On closing the cap, the breath flap is re-set and the disc indexed around by one cavity. The disc is moved around progressively as the cap is closed and it is not clear at what point the breath flap is re-set, nor indeed how the breath flap is re-set. There is potential for the breath flap to be re-set before the disc has been fully indexed, e.g. if the cap is partly closed and then re-opened.